How big of a TT can an Expedition safely handle?

If you have a older expedition , you may want to crawl under and look at the trailing arms on the rear axle . My neighbor drove out of his driveway and one broke , it was rusted , so was the other but , only one broke . He had a 2006 and the rust was only on the trailing arms everything else was fine . He was just lucky it happened there and not driving down the road .